long查询结果转换为varchar2类型

来自Thomas Kyte 《Oracle9i/10g/11g编程艺术》 12章节中.由于long的操作限制,那么在操作long之前可以将该类型的结果转换为varchar2然后再使用,long_help.substr_of的基本意思是将long结果的的前4000字节转换为varchar2类型.如果long的数据超过了4000字节,那么可以将循环调用此函数

create or replace package long_help
authid current_user
as
function substr_of
( p_query in varchar2,
p_from  in number,
p_for   in number,
p_name1 in varchar2 default NULL,
p_bind1 in varchar2 default NULL,
p_name2 in varchar2 default NULL,
p_bind2 in varchar2 default NULL,
p_name3 in varchar2 default NULL,
p_bind3 in varchar2 default NULL,
p_name4 in varchar2 default NULL,
p_bind4 in varchar2 default NULL )
return varchar2;
end;

create or replace package body long_help
as
    g_cursor number := dbms_sql.open_cursor;
    g_query  varchar2(32765);
procedure bind_variable( p_name in varchar2, p_value in varchar2 )
is
begin
    if ( p_name is not null )
    then
        dbms_sql.bind_variable( g_cursor, p_name, p_value );
    end if;
end;

function substr_of
( p_query in varchar2,
  p_from  in number,
  p_for   in number,
  p_name1 in varchar2 default NULL,
  p_bind1 in varchar2 default NULL,
  p_name2 in varchar2 default NULL,
  p_bind2 in varchar2 default NULL,
  p_name3 in varchar2 default NULL,
  p_bind3 in varchar2 default NULL,
  p_name4 in varchar2 default NULL,
  p_bind4 in varchar2 default NULL )
return varchar2
as
    l_buffer       varchar2(4000);
    l_buffer_len   number;
begin
    if ( nvl(p_from,0) <= 0 )
    then
        raise_application_error
        (-20002, 'From must be >= 1 (positive numbers)' );
    end if;
    if ( nvl(p_for,0) not between 1 and 4000 )
    then
        raise_application_error
        (-20003, 'For must be between 1 and 4000' );
    end if;
    if ( p_query <> g_query or g_query is NULL )
    then
        if ( upper(trim(nvl(p_query,'x'))) not like 'SELECT%')
        then
            raise_application_error
            (-20001, 'This must be a select only' );
        end if;
        dbms_sql.parse( g_cursor, p_query, dbms_sql.native );
        g_query := p_query;
    end if;
    bind_variable( p_name1, p_bind1 );
    bind_variable( p_name2, p_bind2 );
    bind_variable( p_name3, p_bind3 );
    bind_variable( p_name4, p_bind4 );
    dbms_sql.define_column_long(g_cursor, 1);
    if (dbms_sql.execute_and_fetch(g_cursor)>0)
    then
        dbms_sql.column_value_long
        (g_cursor, 1, p_for, p_from-1,
         l_buffer, l_buffer_len );
    end if;
    return l_buffer;
end substr_of;
end;

使用方法:查询DBA_TAB_PARTITIONS中的HIGH_VALUE

SELECT *
  FROM (SELECT TABLE_OWNER,
                TABLE_NAME,
                PARTITION_NAME,
                LONG_HELP.SUBSTR_OF('SELECT HIGH_VALUE
FROM   DBA_TAB_PARTITIONS WHERE TABLE_OWNER=:TABLE_OWNER 
AND TABLE_NAME=:TABLE_NAME
AND PARTITION_NAME=:PARTITION_NAME',
                                     1,
                                     4000,
                                     'TABLE_OWNER',
                                     TABLE_OWNER,
                                     'TABLE_NAME',
                                     TABLE_NAME,
                                     'PARTITION_NAME',
                                     PARTITION_NAME) HIGH_VALUE
           FROM DBA_TAB_PARTITIONS);